The invention relates generally to the use of non-conventional forms of carbon black in curable rubber compounds. The non-conventional carbon black generally includes particles in the shape open conical structures to enhance properties of rubber compounds, particularly for use in tires.
Pneumatic rubber tires are conventionally prepared with at least one component, such as, for example, a rubber tread, which is often a blend of various rubbers and reinforced with conventional, granular carbon black. For example, a non-limiting list of such rubbers would include at least one, and more often two or more, of styrene/butadiene copolymer(s) (SBR), cis-1,4-polyisoprene including natural rubber, cis-1,4-polybutadiene and styrene/isoprene/butadiene terpolymer(s) as well as other elastomers. Further, such tires may, for example, have a tread composed of natural rubber, a tread composed of a blend of SBR and cis-1,4-polybutadiene rubbers, a tread composed of natural rubber and SBR as well as treads composed of tri-blends such as SBR (40 to 60 phr) with 20 to 45 percent styrene, cis-1,4-polyisoprene (20 to 30 phr) and cis-1,4-polybutadiene (20 to 30 phr). For example, see The Vanderbilt Rubber Handbook, 13th Edition (1990), Pages 603 and 604.
The characteristics of carbon black are a significant factor in determining various properties of a rubber composition with which the carbon black is compounded. Conventionally, for rubber reinforcement, tire tread rubber compositions use high surface area, elastomeric reinforcing granular carbon blacks for a purpose of providing tread rubber compositions with good traction and abrasion resistance. On the other hand, in order to enhance the fuel efficiency of a motorized vehicle, a decrease in the rolling resistance of the tire tread portion is desirable. There are some indications that this has been achieved, for example, by increasing the resilience of the rubber by using carbon blacks having a large particle diameter and a small surface area or granular carbon blacks having a wide range of aggregate size distribution per given particle diameter.
It is believed to be conventional wisdom that a tire tread composition designed to improve tread traction on the road usually results in a tire""s increased tire rolling resistance. Similarly, modifying a tire tread composition to improve (reduce) a tire""s rolling resistance usually results in a reduction in the tire tread traction and/or treadwear resistance. It is usually difficult to impart both high abrasion resistance and high resilience to the rubber at the same time, because the requirements have been thought to be somewhat contradictory with each other from the perspective of the properties of the granular carbon black in the rubber. These aspects involving a trade-off of tire, or tire tread, properties (traction, rolling resistance and treadwear) are well known to those having skill in such art. Thus, selection of various reinforcing carbon blacks tend to play a role in the ultimate properties of the rubber composition.
For some tire tread applications, silica is used for at least a portion of the rubber reinforcement, often in conjunction with the granular carbon black, and usually accompanied by a silica coupler.
The term xe2x80x9cphrxe2x80x9d as used herein, and according to conventional practice, refers to xe2x80x9cparts of a respective material per 100 parts by weight of rubber elastomerxe2x80x9d. In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d can be used interchangeably, unless otherwise distinguished. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d can be used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The terms xe2x80x9cgranular carbon blackxe2x80x9d are used herein to refer to conventional carbon blacks, the use of which in rubber compositions is well known in the art. Generally, granular carbon black may be characterized as a multiplicity of elementary graphitic particles fused together to form grape-like aggregates familiar to those skilled in the art. Further description of conventional carbon black morphology can be found on Pages 398 through 410 of The Vanderbilt Rubber Handbook, 13th Edition.
In accordance with the present invention, a rubber compound is provided with an amount of conical carbon black for reinforcement, the conical carbon black comprising open conical carbon structures and flat plates.
The invention also relates to a tire having at least one portion composed of a rubber composition which contains, as reinforcement, a conical carbon black comprising open conical carbon structures which is useful as a reinforcement in rubber compounds in place of at least a portion thereof or in addition to, the normally used forms of granular carbon black reinforcement.
Such non-conventional, conical carbon black may be used as discrete particles and/or aggregates and agglomerates of such particles.
The term carbon black is herein used, unless otherwise indicated, in a broad sense to include any particulate graphitic material, including granular carbon blacks conventionally used as reinforcements in tires and rubber as well as other, nonconventional forms of particulate graphite. By carbon black comprising open conical structures, it is meant to be any carbon black comprising open conical carbon structures and flat plates, but may also comprise minor amounts of fullerenes, carbon nanotubes, and other graphitic structures. The terms xe2x80x9cconical carbonxe2x80x9d, xe2x80x9cconical carbon blackxe2x80x9d, xe2x80x9copen conical structuresxe2x80x9d, xe2x80x9ccones and platesxe2x80x9d, xe2x80x9ccones and flat platesxe2x80x9d, and xe2x80x9cmicroconesxe2x80x9d are herein used interchangeably to refer to the unconventional carbon black used in the rubber composition of the present invention.
According to this invention, a tire is provided having a tread of a rubber composition comprised of, based on 100 parts by weight rubber
(A) 100 parts by weight (phr) of at least one diene-based elastomer and
(B) about 10 to about 150, alternatively about 20 to about 100, phr of particulate elastomer reinforcement composed of about five to about 100, alternately about 10 to about 60, weight percent of at least one conical carbon black and from zero to about 95, alternately about 60 to about 10, weight percent of at least one of granular carbon black and, optionally, precipitated silica; wherein said conical carbon black has conical and flat plate shaped particles characterized by a topological disclination TD given by the general formula
TD=Nxc3x9760 degrees, where N=0, 1, 2, 3, 4, or 5
The structure of such conical particles and flat plates can be grossly described as stacks of graphitic sheets with flat (N=0) or conical structures (N=1 to 5), and holding cone angles of 180, 112.9, 83.6, 60.0, 38.9, and 19.2 degrees for each of N=0 to 5, respectively. The characteristic size, or longest dimension, of the particles is typically less that 5 micrometers and the thickness, measured as the wall thickness of the hollow cones or the thickness of the flat plate, is typically less than 100 nanometers. Cones of N=1 to 5, nanotubes, and fullerenes may make up about 20 percent of the conical carbon black, with the remaining about 80 percent being mainly flat plates of N=0. Alternatively, flat plates of N=0, TD=0 and a projected angle of 180xc2x0 may be present as a major fraction of the conical carbon black, that is, in excess of 50 percent by weight. Cones of N=1, 2, 3, 4, or 5, fullerenes, or nanotubes may be present as a minor fraction of the conical carbon black, that is, less than 50 percent by weight.
Alternatively, the elastomer reinforcement may also be composed of (i) about 5 to about 90, alternatively about 10 to about 50, weight percent of said conical carbon black, and correspondingly (ii) about 95 to about 10, alternatively about 90 to about 50, weight percent of at least one reinforcing filler selected from at least one of conventional granular carbon black and precipitated silica.
The conical carbon black is further characterized by having either a nitrogen adsorption number (ASTM D3037) or an Iodine adsorption number (ASTM D1510) of less than 30 g/kg and a DBP number of greater than 150 cm3/100 g. Preferably, the optional granular carbon black has an Iodine adsorption value in a range of about 30 to about 150 g/kg, preferably about 100 to about 150 g/kg for tread rubber, and a DBP Number in a range of about 60 to about 140 cm3/100 g, preferably about 100 to about 140 cm3/100 g for tread rubber, and preferably the optional precipitated silica has a BET surface area as measured using nitrogen gas in a range of about 40 to about 600, preferably 50-300, and a DBP number in a range of about 100 to about 400, more preferably 150-300.
Such conical carbon black having cone and plate shaped particles is considered herein to be substantially open conical and planar in form, and thus, are considered herein to be, basically, extended surfaces of graphitic carbon.
A discussion of carbon having cone and plate shaped particles, herein referred to as conical carbon black, may be reviewed in an article entitled xe2x80x9cGraphitic Cones and the Nucleation of Curved Carbon Surfacesxe2x80x9d appearing in Nature (1997), July 31 issue, and further in PCT publication WO 98/42461.
In one aspect of this invention, conical carbon black can be used by itself as reinforcement for rubber compositions for tire components or it can be used in combination with more conventional granular carbon black(s).
In another aspect of this invention, the conical carbon black, imparting acceptable physical properties to rubber compounds at a lower carbon loading that needed with conventional granular carbon blacks, is used in place of more conventional granular carbon black reinforcements, thereby allowing a reduction of overall tire weight.
In another aspect, a tire is provided with a component such as a tread wherein at least one vulcanizable rubber is combined with a sufficient amount of conical carbon black or a mixture of a conical carbon black and a conventional granular carbon black, to result in a modification of the dynamic properties of the tire component as compared to those of such component for which no conical carbon had been added.
It is still yet another object of this invention to disclose a composition of at least one vulcanizable rubber, preferably at least one sulfur vulcanizable rubber, and a sufficient amount by weight of conical carbon black in comparison to the rubber to result in a modification of the dynamic properties of the rubber compared to those of the rubber without any added conical carbon black. In this embodiment, it is preferred that the tread of the rubber composition be comprised of, based on 100 parts by weight rubber
(A) 100 parts by weight (phr) of at least one diene-based elastomer and
(B) about 10 to about 150, alternatively about 25 to about 60, phr of particulate elastomer reinforcement composed of about five to about 100 weight percent of at least one conical carbon black and from zero to about 95 weight percent of at least one of granular carbon black and precipitated silica; wherein said conical carbon black is characterized by having topological disclination TD given by the general formula
TD=Nxc3x9760 degrees, where N=0, 1, 2, 3, 4, or 5
Alternatively, the elastomer reinforcement may also be composed of (i) about 5 to about 90, alternatively about 10 to about 50, weight percent of said conical carbon black, and correspondingly (ii) about 95 to about 10, alternatively about 90 to about 50, weight percent of at least one reinforcing filler selected from at least one of conventional granular carbon black and precipitated silica. The conical carbon black has an Iodine adsorption number of less than 30 g/kg and a DBP Number of greater than 150 cm3/100 g. Conversely, granular carbon black has an Iodine adsorption value in a range of about 30 to about 150 g/kg, preferably about 100 to about 150 g/kg for rubber reinforcement, and a DBP Number in a range of about 60 to about 140 cm3/100 g, preferably about 100 to about 140 cm3/100 g for rubber reinforcement, and preferably the precipitated silica has a BET surface area as measured using nitrogen gas in a range of about 40 to about 600, preferably 50 to 300, and a DBP number in a range of about 100 to about 400, more preferably 150 to 300.
These and other aspects of this invention will be further understood when viewed in light of the drawings, further detailed description and appended claims.